1) Field of the Invention
This invention relates to a fault diagnosis apparatus and method for a vehicle control system. The fault diagnosis apparatus and method are useful in diagnosing a fault of an electronic component mounted on a vehicle, especially when the fault has led to such a control as deteriorating exhaust gas.
2) Description of the Related Art
It has been the common practice to electronically control the operations of an engine, an automatic transmission (which may hereinafter be abbreviated as "AT") and the like, which are mounted on a vehicle. Their control is however performed based on outputs from plural sensors, resulting in the inconvenience that appropriate control would no longer be feasible if one or more of the sensors fail. To cope with this inconvenience, each automobile maker has adopted its own fault diagnosis method, thereby detecting a fault of a sensor and outputting its own sensor fault signal to its own diagnosis system.
In the meantime, regulations on the emission control (the so-called "OBD-II") have been introduced recently in the United States. Under the regulations, it is required that if control of an automatic transmission mounted on a vehicle is performed in such a way as deteriorating the exhaust gas emitted from the vehicle, a failed electronic component for the AT control, said failed electronic component being responsible for the deteriorated exhaust gas, should be detected and also informed to the driver by turning on an indicator lamp or the like. This applies equally to electronic components for the control of an engine.
According to the above regulations, fault signals independently detected by individual automotive makers are coded in accordance with the communication rules (ISO 9141) specified by the regulations so that when a prescribed diagnosis system is employed, each failed electronic component can be detected as a common signal irrespective of the maker.
Now assume, for example, that a vehicle is equipped with an engine control unit (ECU), an AT control unit and a further control unit for other devices. Where a fault responsible for a deterioration in exhaust gas is detected in one of electronic components of each control unit, it may then be thought of informing the fault by turning on an indicator lamp as described above and further of coding a fault signal in each control unit in accordance with the communication rules prescribed above and then outputting the thus-coded fault signal to a diagnosis system.
This however requires to provide each of the control unit with a conversion unit which can output a coded signal conforming with the prescribed communication system described above, resulting in the problem that the construction becomes complex and a significant increase is unavoidable in the manufacturing cost.